The objective of this proposed study is to investigate those factors which regulate the reversible inactivation and reactivation of kidney adenosine triphosphatase (ATPase). I believe that the data which has been collected in this laboratory supports the thesis that both inactivation of ATPase and the reactivation of the inactivated ATPase are enzyme dependent. It is suggested that the reactivating system is distinct from ATPase. The data has revealed that the total ATPase (mg2 ion - ATPase and Na plus K ions ATPase) can be reversibly inactivated. Furthermore, the inactivated ATPase exhibits a 'lag-phase' in the hydrolysis of ATP. This "conversion of activity" has significant implications in the control of the hydrolysis of ATP and electrolyte transport. Other enzymes undergoing similar types of transformations have been described by others. It is planned to characterize the inactivating and reactivating systems. This study will facilitate the interpretation of the levels of activity of ATPase in vivo and in vitro. Rat kidney microsomal ATPase will be purified. The methodology will include desoxycholate and lubrol solubilization, zonal centrifugation, SDS polyacrylamide gel electrophoresis, column chromatography and iodide treatment. The component required for 'inactivation' of ATPase and the component required for the 'reactivation' of inactivated ATPase will be purified by methods similar to these utilized in the purification of ATPase. The purified system will be reconstructed and various effects will be examined which will include nucleotide specificity, effects of calcium, zinc, temperature, ouabain, pH, the stability and 32P incorporation.